<TITLE>prob018: water bucket problem</TITLE>
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<H1>prob018: water bucket problem</H1>

<TABLE>
<TR> <TD> proposed by
     <TD ALIGN=LEFT> <A HREF="http://www.cs.york.ac.uk/~tw">
          <B>Toby Walsh</B></A> 
          <ADDRESS><a href="mailto:tw@cs.york.ac.uk">
          tw@cs.york.ac.uk</a></ADDRESS>
</TABLE>
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<H3> Specification </H3>

<TT>
Given the promise of SAT and CSP techniques for solving "classical"
planning problems, I decided to propose this puzzle. 
<P>
You are given an 8 pint bucket of water, and two
empty buckets which can contain 5 and 3 pints respectively.
You are required to divide the water into two by pouring
water between buckets (that is, to end up with 4 pints in the 8 pint 
bucket, and 4 pints in the 5 pint bucket). 
<P>
What is the minimum number of transfers of water between
buckets? The challenge is to solve this as a planning problem
(encoded into satisfiability or constraint satisfaction) with
an efficiency approaching (or exceeding) a simple 
<A HREF="enumerate.pl">enumeration</A>.
</TT>


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